The apparatus of the present invention is used for the endoscopic irrigation of body cavities, for example the bladder, the uterus or articular capsules.
The apparatus may be specially used in arthroscopy in an endoscopic resection of a joint. In this connection, a physiological liquid is pumped by means of an irrigation pump through an irrigation conduit into the joint. The liquid is then drawn off from the joint by means of a suction pump through a suction conduit.
It is desirable during such an endoscopic irrigation of hollow organs that the pressure and the flow rate of the irrigation liquid in the body cavity can be adjusted independently from one another. The flow rate is to be understood as the liquid volume through the body cavity per time unit.
U.S. Pat. No. 4,902,277 (“the '277 patent”) discloses a system for irrigating a body cavity utilizing an irrigation pump with a feed conduit connected to a body cavity for feeding fluid into the body cavity and a suction pump connected to a suction conduit for removing fluid from the body cavity. A pressure transducer controls the irrigation pump while a speed transducer controls the suction pump.
However, a major disadvantage the '277 patent is observed when an obstruction which is, for example, caused by tissue pieces, occurs in the suction conduit. In case of an obstruction in the suction conduit, the actual pressure in the body cavity may exceed the nominal pressure with the result that the irrigation pump of the known apparatus is controlled such that its speed decreases, in order to maintain the nominal pressure. In contrast to that, the suction pump that is adjusted to the predetermined nominal flow rate, works on with an unchanged speed. The result is that the suction pump does not work harder to draw off the obstruction and the irrigation pump eventually shuts down as pressure increases leaving the body cavity pressurized. This can lead to a disturbance and interruption of the irrigation operation and, thereby, of the medical operation. Therefore, it is undesirable to control the suction pump with a speed control or control the irrigation pump with a pressure transducer.
On the other hand, an apparatus for irrigating a body cavity is known from EP 0 529 902 A2, the irrigation pump of which is a centrifugal pump, which is controlled as a function of a predetermined nominal pressure in the body cavity or in the irrigation conduit, respectively, while the suction pump is a displacement pump in form of a gear pump. Unlike a displacement pump, a centrifugal pump has the characteristic that the produced flow rate is not a single-valued function of the speed of the centrifugal pump, but in addition depends on the actual pressure. With this known apparatus, the flow rate is adjusted by means of a controllable tube-squeezing valve.
However, EP 0 529 902 A2 has the disadvantage that the irrigation pump, which is designed as a centrifugal pump, is not sealing so that in case that the squeezing valve is not closed and both pumps are not activated, the liquid can flow through without impediment as a result of the gradient. Another disadvantage of EP 0 529 902 A2 is, as mentioned before, that by using a centrifugal pump as the irrigation pump, the flow rate cannot be preset in exact manner because neither the irrigation pump nor the suction pump allow a simple dependency of the flow rate, for example as a function of the speed of the pumps. In this known apparatus, the actual flow rate highly depends on the pressure difference in the system.
It is an object of the invention to provide an apparatus of the afore-mentioned kind by means of which the pressure and the flow rate can be controlled as independently from each other as possible.